1. Field of the Invention
The present invention relates to a sealing resin-metal assembly for use as a cushion material, a packing material or a spacer for electric and/or electronic components, and more particularly to a sealing resin-metal assembly preferable for use as a fuel cell separator.
2. Description of the Related Art
In recent years, polymer electrolyte membrane fuel cells have drawn attentions as a power source for electric vehicles. Polymer electrolyte fuel cells (PEFC) can generate power even at ordinary temperatures and therefore are being put in practical use for various applications.
In general, a fuel cell system is a system constructed such that a polymer electrolyte membrane is held between a cathode electrode and an anode electrode with the cathode electrode being disposed on one side of the polymer electrolyte membrane and the anode electrode on the other side thereof. An external load is driven by power generated through a chemical reaction between oxygen in air supplied to the cathode electrode and hydrogen supplied to the anode electrode.
A fuel cell stack 100 as shown in FIG. 10A is provided in the fuel cell system. The fuel cell stack 100 is constituted by a number of single cells each adapted to generate power with a membrane being held therein, which are stacked repeatedly in many stages in a horizontal direction in such a manner that the surfaces of the electrodes are oriented vertically and are then fastened together with bolts.
As shown in FIG. 10B, the single cell is constituted by a polymer electrolyte membrane M, electrode catalyst layers C, C, gas diffusion layers D, D, an air-side separator SA and a hydrogen-side separator SH.
Of these constituent components, the separators SA, SH are used for links (stacking function) between respective single cells which are stacked in a plural number for generation of a required voltage.
In addition, the separators SA, SH are required to have other functions, and they are:
(1) To secure, within the fuel cell stack 100, supply passages for supplying hydrogen and air to the cells;
(2) To secure supply passages for supplying coolant for cooling the fuel cell stack 100; and
(3) To collect and take out current (flow of electrons).
To make them happen, since conductivity and corrosion resistance are required for materials for the separators SA, SH, carbon materials which are mixtures of synthetic graphite or graphite and resin are used.
However, using carbon materials as the separators SA, SH deteriorates the productivity and therefore, in recent years metallic materials have been studied with a view to reducing costs.
In addition, as a seal material for use in laminating the separators SA, SH, as shown in FIG. 10B, a rubber seal material (fluorine system, EPDM or the like) RS, which is formed separately from the separators SA, SH, is inserted to be interposed between the air-side separator SA and the hydrogen-side separator SH so as to function as a cushion material, a packing material, a spacer and a gas leakage preventive seal material.
However, with this sealing method, lots of man-hours are required in assembling a fuel cell stack 100 by stacking single cells, and as a result, there have been caused problems that the production costs of fuel cell stacks 100 are increased and that the safety of fuel cell stacks 100 is damaged by virtue of a failure in assembling the rubber seal material RS.
Then, raised as an improved technique to solve these problems is a technique disclosed in JP-A-11-129396. The technique so disclosed relates to a silicone resin-metal composite material in which a sealing resin layer (packing material) and a metallic material are incorporated.
In this metallic separator, a silicone resin layer having a thickness ranging from 0.05 mm to 1.0 mm and a hardness (JIS K 6301—spring hardness test, A type) ranging from 40 to 70 is injection molded on at least one side of a sheet metal.
The metallic separator provides, however, the following problems at the time of injection molding the silicone resin layer:
(1) While burrs and bubbles are not generated depending upon operating conditions at the time of injection molding, the applicable operating conditions are limited. Further, since liquid silicone is used as a raw material for the silicone layer, when shifting from the operating condition, a leakage of liquid silicone from the interior to the exterior of the die cannot successfully be prevented, and liquid silicone that has so leaked expands to the periphery of the die to form burrs thereat; and
(2) In order to prevent the occurrence of burrs, the clamping force of the die needs to be increased to eliminate a gap between the die and the sheet metal. However, increasing the clamping force deforms the sheet metal.